Both guns share some parts like the gas systems. The SX2 has a high rib while the Gold has a low rib. The Gold has more features like a magazine cutoff, speed load, and a larger triangle safety. They also cost about $100.00 over the SX2. If you don't want the extra features and like the high rib get the the SX2, otherwise get the Gold. Eirther way is a good choice.
Both have a $100.00 rebate till the end of November.
I'd take a SX2 or Franchi 912 over an 11-87 any day. They are priced similar, but much better in terms of reliabilty, quality, features, weight and balance.